[Elecraft] Elecraft KX3 Owner's Manual nowavailable(*preliminary*)

[Oliver Dröse]

> The advantage is that I could possibly pull out the RTS line from my one 
> RS232 cable
> to the computer, and simply add it to the amplifier PTT plug in ACC2.  I 
> would not
> have to build a transistor switch to directly trigger the PTT line, which 
> would have
> to be broken out from the custom MIC plug.

Hi Lance,

you should *NOT* apply RTS directly to the GPIO pin! RS-232 levels go up 
into the +/-20 volts region per specs and that would probably damage the 
microcontroller in the KX3 (at least this pin). Maybe Wayne can shine some 
light onto if GPIO is directly connected to the MC and thus can only accept 
5 V or if there is something else in-between.

Please don't be mistaken by that you can apply RTS directly at the K3 
because that has a level converter built in active also for RTS/DTR pins 
while the KX3 probably won't (see above).

So an "interface" is needed anyway (1-transistor-interface), that's why I 
originally asked what the advantage of using GPIO for PTT would be (besides 
maybe easier cabling).

A better solution might be to simply use VOX on DATA A then also for WSJT 
(just for easier cabling, I would still prefer "real" PTT on the mic 
connector) and use GPIO's TX-INHIBIT functionality together with a smallish 
sequencer (could be built into the amp, too). Then you could be sure that 
the radio is not putting out any HF before all other equipment (PA, pre-amp, 
etc.) has switched and the TX-INH is unlocked. I am doing exactly that on my 
K3 ... and others, too. ;-))

Vy 73, Olli - DH8BQA
http://www.dh8bqa.de